Method and apparatus of operating devices using actuators having expandable or contractable elements

ABSTRACT

An apparatus and method of operating devices (such as devices in a wellbore or other types of devices) utilizes actuators having expandable or contractable elements. Such expandable or contractable elements may include piezoelectric elements, magnetostrictive elements, and heat-expandable elements. Piezoelectric elements are expandable by application of an electrical voltage; magnetostrictive elements are expandable by application of a magnetic field (which may be generated by a solenoid in response to an electrical current); and heat-expandable elements are expandable by heat energy (e.g., infrared energy or microwave energy). Expandable elements are abutted to an operator member such that when the expandable element expands, the operator member is moved in a first direction, and when the expandable element contracts, the operator member moves in an opposite direction.

BACKGROUND

[0001] The invention relates to methods and apparatus of operatingdevices (such as devices in wellbores) using actuators having expandableor contractable elements.

[0002] In a well, various devices may be activated to perform differenttasks. Downhole devices may include valves (e.g., flow control valves orsafety valves), perforating guns, and other completion components.Different forms of activation mechanisms, including hydraulic,mechanical, or electrical mechanisms, may be used. Mechanical activationtypically involves lowering some type of setting or shifting tool to adesired depth to engage the downhole device to apply a force to move anactuator operably coupled to the downhole device. Hydraulic activationtypically involves application of hydraulic pressure either through atubing, a tubing-casing annulus, or a hydraulic control line to anactuator in a downhole device. Electrical activation typically involvescommunicating electrical power and/or signaling down an electricalcable, such as a wireline, an electrical control line, or other type ofelectrical line to a downhole actuator, which may include an electroniccontroller, a motor, or a solenoid actuator.

[0003] Conventional electrical actuators, such as solenoid actuators,typically require large amounts of electrical current to operate.Communication of high electrical currents may require relatively heavyelectrical cables, which may be difficult to handle and which may takeup too much space in a wellbore. Further, in some actuators, relativelysophisticated downhole electronic circuitry may be used. Such electroniccircuitry may have reliability problems. Other types of actuators mayalso be associated with various issues. For example, mechanicalactuators may be time-consuming and difficult to operate. Hydraulic andother fluid pressure actuators require a fluid pressure communicationspath, which may be impractical in certain parts of the wellbore. Also,leaks may develop that would render the hydraulic or other fluidpressure actuator inoperable.

[0004] A need thus continues to exist for improved actuators foroperating downhole devices and other types of devices.

SUMMARY

[0005] In general, according to one embodiment, an apparatus foroperating a downhole device in a wellbore includes an actuator havingone or more elements expandable by input energy and an operatormechanism operably coupled to the actuator.

[0006] Other embodiments and features will become apparent from thefollowing description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 illustrates an embodiment of a completion string having asubsurface safety valve in a wellbore.

[0008]FIG. 2 illustrates an actuator having piezoelectric elements thatare expandable in response to an applied input voltage in accordancewith an embodiment.

[0009]FIG. 3 illustrates an actuator having a magnetostrictive elementthat is expandable in response to an applied magnetic field inaccordance with another embodiment.

[0010]FIGS. 4 and 5 illustrate a rotary motor employing actuators ofFIG. 2.

[0011]FIG. 6 illustrates an actuator having a heat-expandable element inaccordance with yet another embodiment.

[0012]FIG. 7 is a longitudinal sectional view of a subsurface safetyvalve assembly including actuators of FIG. 6 in accordance with oneembodiment.

[0013]FIG. 8 is a more enlarged sectional view of a portion of thesubsurface safety valve assembly of FIG. 7.

[0014]FIG. 9 is a timing diagram including an input signal and waveformsrepresenting activation of the actuators of FIGS. 7 and 8.

DETAILED DESCRIPTION

[0015] In the following description, numerous details are set forth toprovide an understanding of the present invention. However, it will beunderstood by those skilled in the art that the present invention may bepracticed without these details and that numerous variations ormodifications from the described embodiments may be possible.

[0016] As used here, the terms “up” and “down”; “upper” and “lower”;“upwardly” and downwardly”; and other like terms indicating relativepositions above or below a given point or element are used in thisdescription to more clearly described some embodiments of the invention.However, when applied to equipment and methods for use in wells that aredeviated or horizontal, such terms may refer to a left to right, rightto left, or other relationship as appropriate.

[0017] Referring to FIG. 1, a completion string in accordance with oneexample embodiment is positioned in a wellbore 10. The wellbore 10 maybe part of a vertical well, deviated well, horizontal well, or amultilateral well. The wellbore 10 may be lined with casing 14 (or othersuitable liner) and may include a production tubing 16 (or other type ofpipe or tubing) that runs from the surface to a hydrocarbon-bearingformation downhole. A production packer 18 may be employed to isolate anannulus region 20 between the production tubing 16 and the casing 14.

[0018] A subsurface safety valve assembly 22 may be attached to thetubing 20. The subsurface safety valve assembly 22 may include a flappervalve 24 or some other type of valve (e.g., a ball valve, sleeve valve,disk valve, and so forth). The flapper valve 24 is actuated opened orclosed by an actuator assembly 26. During normal operation, the valve 24is actuated to an open position to allow fluid flow in the bore of theproduction tubing 16. The actuator assembly 26 in the safety valveassembly 22 may be activated by signals in a control line 28 (e.g., anelectrical cable, fiber optic line, waveguide, and so forth) that runsup the wellbore 10 to a controller 12 at the surface. The safety valve24 is designed to close should some failure condition be present in thewellbore 10 to prevent further damage to the well.

[0019] Although the described embodiment includes an actuator used witha subsurface safety valve, it is contemplated that further embodimentsmay include actuators used with other types of downhole devices. Suchother types of downhole devices may include, as examples, flow controlvalves, packers, sensors, pumps, and so forth. Other embodiments mayinclude actuators used with devices outside the well environment.

[0020] In accordance with some embodiments of the invention, theactuator assembly includes one or more expandable elements that areexpandable by an input energy. Such expandable elements may includepiezoelectric elements, magnetostrictive elements, and heat-expandableelements. Other types of expandable elements may also be employed. Theexpandable elements are adapted to move an operator member, which may bedirectly or indirectly connected to a downhole device to be actuated. Infurther embodiments, contraction of such elements may be used to actuatedownhole devices. For example, the elements may initially be maintainedin an expanded state, with input energy removed to contract the elementsfor device actuation.

[0021] In accordance with further embodiments, the actuator assembly mayinclude at least a first actuator and a second actuator. The firstactuator (referred to as an operating actuator) is adapted to move theoperator member in incremental steps, while the second actuator(referred to as a holding or latching actuator) is adapted to latch ormaintain the operator member in its current position after eachincremental move. The first actuator is alternately activated anddeactivated at a predetermined frequency by cycling an input activationenergy between on and off states at the predetermined frequency. Eachcycle of activation and deactivation of the first actuator moves theoperator member by a predetermined incremental displacement. The firstand second actuators may be associated with different frequencyresponses such that cycling of the activation energy at thepredetermined frequency causes the first actuator to turn on and off butallows the second actuator to be maintained in an energized condition.Each of the first and second actuators may be associated with a timeconstant, with the time constant of the second actuator being greaterthan that of the first actuator. Depending on the type of expandableelement, the activation energy may be electric energy, magnetic energy,heat energy, infrared energy, microwave energy, or other forms ofenergy.

[0022] Referring to FIG. 2, an actuator 300 includes piezoelectricelements each expandable by application of an input electrical voltageacross the element. The actuator 300 may be referred to as apiezoelectric linear motor. One type of piezoelectric material is leadzirconate titanate. Another type of piezoelectric material includesBaTiO₃. Generally, the change in length of a piezoelectric material isproportional to the square of the applied voltage.

[0023] A housing 302 in the actuator 300 contains layers of conductors308, 310, insulators 304, and piezoelectric disks 306. Eachpiezoelectric disk 306 is sandwiched between a first conductor plate 308and a second conductor plate 310, with the conductor plates 308 and 310coupled to an input voltage. The insulator layers are placed betweenadjacent conductors 308, 310 to provide electrical isolation. Toactivate the actuator 300, the input voltage is applied to the conductorplates 308 and 310. This causes the piezoelectric disks 306 to expand inan axial direction, generally indicated as X.

[0024] The actuator 300 includes a first ratchet mechanism 312 (referredto as a static or holding ratchet mechanism) and a second ratchetmechanism 314 (referred to as an operating ratchet mechanism). In oneembodiment, each of the ratchet mechanisms 312 and 314 may includeBelleville springs 315 each arranged at an angle such that sharp tips316 of the Belleville springs 315 can grip the outer wall of a shaft 318that is part of the operator member of a downhole device. Instead ofBelleville springs 315, other forms of engagement tablets may be used toengage the shaft 318. Spacers 317, 321, 323, and 322 having generallytriangular cross-sections are positioned to arrange the Bellevillesprings 315 at the desired angle with respect to the outer surface ofthe shaft 318. Spacers 319 are placed between adjacent Bellevillesprings or tablets 315. A spring 320 placed between the spacer 322 andapplies a force against the spacer 322 in a general direction oppositeto the X direction.

[0025] In operation, an input activation voltage that cycles between anon state and an off state is applied to the actuator 300. Application ofthe activation voltage causes the piezoelectric disks 306 to expand tomove the operating ratchet mechanism 314 so that the shaft 318 is movedby a predetermined incremental distance. Removal of the activationvoltage causes the piezoelectric disks 306 to contract so that theoperating ratchet mechanism 314 is moved backward by action of thespring 320. The shaft 318, however, is maintained in position by thestatic or holding ratchet mechanism 312. Subsequent cycles of theactivation voltage causes the shaft 318 to move forward (in generallythe X direction) by incremental steps. This provides a simple “inchworm” type of linear motor.

[0026] In other embodiments, the actuator 300 may be arrangeddifferently. For example, instead of multiple piezoelectric disks 306, asingle piezoelectric element may be used. Further, in anotherarrangement, the holding ratchet mechanism 312 may be omitted. Inanother arrangement, a ratchet mechanism may be designed such that itengages a shaft or another type of operator member when thepiezoelectric element or disks expand and disengages from the shaft oranother type of operator member when the piezoelectric element or diskscontract. Many other types of arrangements are also possible.

[0027] Referring to FIG. 3, in accordance with another embodiment, anactuator 400 includes an expandable element formed of a magnetostrictivematerial that changes its dimensions in response to an applied magneticfield. One example of a magnetostrictive material is Terfenol-D, whichis a special rare-earth iron material that changes its shape in responseto an applied magnetic field. Terfenol-D is a near-single crystal of thelanthanide elements terbium and dysprosium plus iron. Another type ofmagnetostrictive material includes nickel or a nickel alloy.

[0028] The actuator 400 includes a housing 402 containing a staticratchet mechanism 412 and an operating ratchet mechanism 414, similar tomechanisms 312 and 314 in FIG. 2. However, instead of piezoelectricdisks 306, the actuator 400 includes a magnetostrictive cylinder 406that is surrounded by a solenoid coil 404 connected to electrical wires401. Application of electrical energy into the coil 404 causesgeneration of a magnetic field. In response to the presence of themagnetic field, the magnetostrictive cylinder 406 expands in generallythe X direction (as well as in other directions). Expansion of themagnetostrictive cylinder 406 causes movement of the operating ratchetmechanism 414 to move the shaft 418 by an incremental step.

[0029] Other arrangements of the actuator 400 are also possible. Forexample, instead of a singular magnetostrictive element 406, multipleelements may be used. Also, the interaction between the magnetostrictiveelement 406 and one or more ratchet mechanisms or other types ofoperator mechanisms may be different in further embodiments.

[0030] Referring to FIGS. 4 and 5, in accordance with anotherembodiment, a plurality of actuators 300 (or alternatively, actuators400) may be used to rotate a cylindrical sleeve 550 to provide arotary-type motor 500. The plurality of actuators 300 may be positionedin cavities 552 formed in a housing 554 of the motor 500. In theillustrated embodiment, the actuators 300 are arranged around the outercircumference of the sleeve 550. The number of actuators 300 useddepends upon the desired actuation force. Input signals provided to theactuators 300 in the illustrated arrangement causes clockwise rotationof the sleeve 550. A different arrangement of the actuators 300 mayrotate the sleeve 350 in the opposite direction. In a furtherembodiment, the actuators 300 may be arranged to contact the inner wallof the sleeve 550.

[0031] Referring to FIG. 6, in accordance with yet another embodiment,an actuator 600 includes an expandable element 602 that is expanded byapplication of some type of heat energy, such as infrared energy ormicrowave energy. Examples of heat-expandable materials includealuminum, shape-memory alloys (e.g., Nitinol), and other materials. Theinfrared or microwave energy may be propagated down a waveguide or fiberoptic line 604. The expandable element 602, generally tubular in shape,is positioned inside a bore of a cylindrical insulator 606 that providesheat insulation. One end 610 of the expandable material 602 is exposedto an end of the waveguide 604. A generally conical cut 612 is formedproximal the end 610 of the expandable element 602 to increase thesurface area that is exposed to energy propagated down the waveguide orfiber optic line 604.

[0032] The other end 608 of the expandable element 602 is in abutmentwith an output rod 614, which is formed of an insulating material. Theoutput rod 614 is part of an operator member for a device to beactuated. To activate the actuator 600, infrared or microwave energy ispropagated down the waveguide or fiber optic line 604, which may berouted down a control line from the surface, to heat up the expandableelement 602. Heating the expandable element 602 causes expansion in theaxial direction to move the output rod 614. A spring (not shown) may beprovided to apply a force against the expandable element 602 so that,when energy is removed from the waveguide or fiber optic line 604 andthe expandable element 602 is allowed to cool, the spring may move theoutput rod 614 back as the expandable element 602 contracts.

[0033] The actuator 600 as shown in FIG. 6 can be used in pairs, withone being an operating actuator and the other one being a holdingactuator. The operating actuator may be used to move an operator memberin incremental steps, as the input energy is cycled between on and offstates. The holding actuator is designed to remain activated to maintainor latch the current position of the operator member. Theheat-expandable elements 602 in the operating and holding actuators 600may be designed to have different time constants. This may be performedby varying the mass of the expandable element 602. Alternatively, theamount of insulation 606 may be varied to vary the time constant. Thus,as the heat energy provided down the waveguide 604 is periodicallyactivated and deactivated, the heat-expandable element 602 of theoperating actuator responds by expanding and contracting. However, theexpandable element 602 of the holding actuator remains in an expandedcondition since it is designed to have a larger time constant and thusrequires a longer time to respond to the change in input energy.

[0034] Similarly, the actuators 300 and 400 containing the piezoelectricand magnetostrictive elements, respectively, may be used in pairs(operating and holding actuator pairs). The designs of the actuators 300and 400 may be modified by removing the static ratchet mechanism (312and 412, respectively) in each. Further, the operating ratchet mechanism(314 or 414) may be modified so that expansion and contraction of theexpandable element 306 or 406 moves the operating ratchet mechanism 314and 414 into or out of engagement with the operator member of the deviceto be actuated.

[0035] The time constants of the piezoelectric or magnetostrictiveelements in the actuators 300 and 400, respectively, may be varied byvarying the amounts of the material used in the holding and operatingactuators. Thus, the operating actuator 300 or 400 may be designed tohave an expandable element with a lower time constant; that is, it iscapable of expanding and contracting at a relatively higher rate. Theholding actuator 300 or 400, on the other hand, includes an expandablematerial with a higher time constant; that is, the material expands andcontracts at a relatively slower rate. The variation of the timeconstants may be performed by varying the masses of the materials. Thisallows the operating actuator 300 or 400 to cycle between expanded andcontracted states while the holding actuator 300 or 400 remains in anexpanded state.

[0036] Referring to FIG. 7, the subsurface safety valve assembly 22 inaccordance with one embodiment includes actuators having heat-expandableelements (such as in actuator 600 in FIG. 6). The safety valve assembly22 includes a housing 104 having at its upper and lower ends threadedconnections for connection to other downhole equipment, such as theproduction tubing 16 (FIG. 1). The housing 104 defines an inner bore 110that is in communication with the bore of the production tubing 16 toenable fluid flow when the valve 24 is open. The housing 104 alsodefines a side conduit 106 in which a waveguide or fiber optic line maybe run to an actuator mechanism 108 that is part of the actuatorassembly 26. During normal operation of the well, the actuator assembly26 maintains the valve 24 open to allow production fluids to flowthrough the bore 110 up to the production tubing 16.

[0037] In accordance with one embodiment, the actuator mechanism 108includes at least two actuators 112 and 114 (each includingheat-expandable elements). Such actuators are referred to asheat-controlled actuators. A heat-controlled actuator operates byapplying input heat energy (e.g., infrared or microwave energy) to aheat-expandable element to move an operator member.

[0038] Both the first and second heat-controlled actuators 112 and 114are coupled to a ratchet sleeve 116. The outer circumference of theratchet sleeve 116 has a teeth profile 117 that is engageable by theheat-controlled actuators 112 and 114. The lower end of the ratchetsleeve 116 is connected to a flow tube 118 that is adapted to operatethe flapper valve 24 between an open or closed position. The flow tube118 has an inner bore (that is coaxial with the bore 110 of the housing104) in which fluid may flow. A spring 120 provides an upwardly actingforce against a flange portion 122 connected to the flow tube 118. Thespring 120 is designed to move the flow tube 118 upwardly to close theflapper valve 24 in the absence of an activation energy to theheat-controlled actuators 112 and 114. The flapper valve 24 rotatesabout a pivot 124. As shown in FIG. 7, the flapper valve 24 is in itsopen position. If the flow tube 118 is allowed to rise, the flappervalve 24 rotates about its pivot 124 to the closed position.

[0039] To open the flapper valve 24, heat energy provided down thecontrol line 28 (e.g., a waveguide or fiber optic line) is communicatedto both the first and second actuators 112 and 114. The input heatenergy is cycled on and off and may be in the form of a square wave,sinusoidal, sinusoidal, or other signal. Another type of input signalingmay include a train of pulses. In accordance with one embodiment, theheat-controlled actuator 112 is adapted to move the ratchet sleeve 116(and thereby the flow tube 118) downwardly in incremental steps. Eachcycle of heat energy applied in the control line 28 moves the ratchetsleeve 116 down by a predetermined incremental distance. Because theratchet sleeve 116 and the flow tube 118 are moved by a relatively smalldistance, the heat energy needed to operate the actuator 112 may bereduced to allow low power actuation of the subsurface safety valveassembly 22.

[0040] The second heat-controlled actuator 114 is adapted to maintainthe position of the ratchet sleeve 116 once it has been movedincrementally by the first heat-controlled actuator 112. Thus, eachcycle of heat energy activates the first heat-controlled actuator 112 tomove the ratchet sleeve 116 down by the predetermined incrementaldistance, followed by deactivation of the first heat-controlled actuator112. The frequency response characteristics of the first and secondsolenoid actuators 112 and 114 and the frequency of the input heatsignal are selected such that the first heat-controlled actuator 112turns on and off in response to the input signal but the secondheat-controlled actuator 114 remains in an activated state to maintainthe position of the ratchet sleeve 116. By maintaining the secondheat-controlled actuator 114 activated and engaged to the ratchet sleeve116, heat energy may be removed from the first actuator 112 to start thenext actuation cycle. This continues until the ratchet sleeve 116 andflow tube 118 have moved downwardly by a sufficient distance to fullyopen the flapper valve 24. The first actuator 112 may be referred to asan operating actuator while the second actuator 114 may be referred toas a holding actuator or a latching actuator.

[0041] Referring further to FIG. 8, the heat-controlled actuators 112and 114 and the ratchet sleeve 116 are illustrated in greater detail.The teeth profile 117 formed on the outer circumference of the ratchetsleeve 116 includes a plurality of teeth 130. Each tooth 130 isgenerally triangular in shape with a generally perpendicular (to theaxis of the ratchet sleeve 116) edge 131 and a slanted edge 133 toprovide a ratchet mechanism, as further described below.

[0042] The operating heat-controlled actuator 112 includes an insulatorcylinder 132 that surrounds a heat-expandable element 134. Theheat-expandable element 134 is expandable in a longitudinal directioninside the insulator 132. The element 134 is abutted to a control rod136 that is connected to a hook 138 to move an engagement member 140into or out of engagement with a tooth 130 of the ratchet sleeve 116.The lower end of the engagement member 140 is pivotally connected at apivot 139 to the housing 104 of the safety valve assembly 22. When thecontrol rod 136 is moved downwardly, the engagement member 140 is pushedtoward the tooth 130 to engage the ratchet sleeve 116. Upon engagementof the member 140 to a tooth 130 of the ratchet 116, further downwardmovement of the control rod 136 by the heat-expandable element 134 movesthe ratchet sleeve 116 down by some predetermined distance. When energyis removed from the heat-expandable element 134, a spring 142 positionedin an annular space around the control rod 136 pushes the rod 136upwardly to its initial reset position as the element 134 contracts.Upward movement of the control rod 136 causes the engagement member 140to disengage from the tooth 130 of the ratchet sleeve 116.

[0043] The holding heat-controlled actuator 114 includes an insulatorcylinder 150 that surrounds a heat-expandable element 152. The lower endof the heat-expandable element 152 is abutted to a control rod 154,which in turn is connected to a ratchet engagement member 156. A spring158 is provided in an annular space around the control rod 154 to pushthe rod 154 upwardly when the heat-expandable element 152 is in itscontracted state.

[0044] Application of heat energy to the heat-expandable element 152causes expansion of the element 152 in a longitudinal direction. Theexpansion of the element 152 causes a corresponding downward movement ofthe control rod 154 and ratchet engagement member 156. The element 152,control rod 154, and ratchet engagement member 156 are moved by asufficient distance to engage a tooth 130 of the ratchet sleeve 116.However, the holding heat-controlled actuator 114 is not designed tomove the ratchet sleeve 116. Rather, the holding heat-controlledactuator 114 is used to maintain or latch the position of the ratchetsleeve 116 after it has been moved by the operating actuator 112. As aconsequence, the heat energy requirement of the holding actuator 114 canbe lower than the energy requirement of the operating actuator 112,resulting in lower energy requirements of the heat-controlled actuationmechanism 108.

[0045] As shown in FIG. 8, the operating heat-controlled actuator 112 isin the engaged position (element 134 expanded) and the holdingheat-controlled actuator 114 is in the disengaged position (element 152contracted). This, however, does not necessarily reflect actualoperation of the actuators 112 and 114, since presence of an inputactivation heat energy may activate both actuators in one embodiment.However, in a further embodiment, separate input signals may be providedto the actuators 112 and 114 for independent control.

[0046] In operation, to open the flapper valve 24, an input signal (heatenergy) is applied down the control line 28 to the heat-controlledactuators 112 and 114 to energize both of the heat-expandable elements134 and 152. As a result, the elements 134 and 152 expand and respectivecontrol rods 136 and 154 are moved downwardly to engage the first andsecond ratchet engagement members 140 and 156 to the next tooth 130 ofthe ratchet sleeve 116. Further increase in the amount of energy downthe control line 28 causes the element 134 in the operating actuator 112to expand more to move the control rod 134 downwardly to move theratchet sleeve 116 by a predetermined incremental distance. Energy maythen be removed from the control line 28 followed by the nextactivation/deactivation cycle a predetermined time period later.

[0047] The heat-controlled actuators 112 and 114 may be designed withdifferent time constants to provide for different frequency responses.For example, the mass of the heat-expandable element 152 may berelatively large to provide a large time constant. On the other hand,the mass of the heat-expandable element 134 may be less than that of theelement 152 to provide a smaller time constant. The different timeconstants of the first and second elements 134 and 152 enable differentfrequency responses of the actuators 112 and 114. Thus, if an inputsignal is cycled at a predetermined rate that is greater than the timeconstant of the first heat-expandable element 134 but less than the timeconstant of the second heat-expandable element 152, energy can be cycledto expand and contract the first element 134 (associated with theoperating actuator 112) while the second element 152 (associated withthe holding actuator 114) remains in an expanded state.

[0048] When the holding actuator 114 is energized, it prevents upwardmovement of the ratchet sleeve 116 to prevent resetting of the valveassembly 22 when heat energy is removed to deactivate the operatingactuator 112 during the inactive portion of an input signal cycle. Dueto the slanted edges 133 of the teeth 130, the operating actuator 112can continue to move the ratchet sleeve 116 downwardly in incrementalsteps even though the holding actuator 114 is engaged to the ratchetsleeve 116. Downward shifting of the ratchet sleeve 116 allows theholding actuator 114 to engage successive teeth 130 in the teeth profile117 until the operating actuator 112 has moved the valve 24 to the openposition.

[0049] In further embodiments, the operating and holding actuators 112and 114 may include piezoelectric or magnetostrictive expandableelements instead of heat-expandable elements. The design can be modifiedsuch that the input energy provided is electrical energy. The electricalenergy may be provided directly to piezoelectric elements to expand suchelements. With a magnetostrictive design, the electrical energy may beprovided to a solenoid that generates a magnetic field to expand themagnetostrictive elements. In either case, the input electrical signalmay be cycled at a predetermined frequency such that the operatingactuator 112 (including piezoelectric or magnetostrictive elements) mayexpand and contract in response to the input signal. In the holdingactuator 114, the piezoelectric or magnetostrictive elements may have atime constant selected such that it does not respond as quickly to theinput signal as the elements in the operating actuator 112. As a result,the piezoelectric or magnetostrictive elements in the holding actuator114 remain in an expanded state to allow latching of the ratchet sleeve116.

[0050] In other embodiments, the holding actuator may not necessarilyinclude an expandable element. Instead, the holding actuator may be amechanical retainer element.

[0051] Referring to FIG. 9, various waveforms representing an inputactivation energy and relative actuation states of operating and holdingactuators are illustrated. An input signal 700 having a square waveformis provided, which may represent electrical energy, magnetic energy,infrared energy, microwave energy, or another form of energy. Theduration of the initial pulse of the input signal 700 is larger thansubsequent pulses to activate both the operating and holding actuators.The activation of the operating actuator is shown by waveform 702, whilethe activation of the holding actuator is shown by the waveform 704.Because the time constant of the holding actuator is larger than that ofthe operating actuator, it takes a longer time for the holding actuatorto activate. A threshold level 706 shows the threshold above which theactuators are considered to be activated (that is, expandable elementsare in the expanded state). After the initial larger pulse, the inputsignal 700 is subsequently cycled between on and off states at apredetermined frequency. This activates and deactivates the operatingactuator, as shown by the waveform 702. However, due to the larger timeconstant of the holding actuator, the activation level of the holdingactuator does not fall below the actuation threshold 706.

[0052] While the invention has been disclosed with respect to a limitednumber of embodiments, those skilled in the art, having the benefit ofthis disclosure, will appreciate numerous modifications and variationstherefrom. It is intended that the appended claims cover all suchmodifications and variations as fall within the true spirit and scope ofthe invention.

What is claimed is:
 1. An apparatus for use in a wellbore, comprising: aratchet mechanism; an activable member responsive to input energy, theactivable member including a material expandable by the input energy;and an operator mechanism actuatable by the ratchet mechanism inresponse to expansion of the material.
 2. The apparatus of claim 1,wherein the material includes a piezoelectric material.
 3. The apparatusof claim 2, wherein the piezoelectric material includes pluralpiezoelectric disks.
 4. The apparatus of claim 2, wherein the inputenergy includes electrical energy.
 5. The apparatus of claim 1, whereinthe material includes a magnetostrictive material.
 6. The apparatus ofclaim 5, wherein the input energy includes magnetic energy.
 7. Theapparatus of claim 6, further comprising a solenoid to generate themagnetic energy in response to an electrical signal.
 8. The apparatus ofclaim 1, wherein the material includes a heat-expandable material. 9.The apparatus of claim 8, wherein the input energy includes heat energy.10. The apparatus of claim 8, wherein the input energy includes one ofinfrared energy and microwave energy.
 11. The apparatus of claim 1,comprising a linear motor including the ratchet mechanism, the activablemember, and the operator mechanism.
 12. The apparatus of claim 1,comprising a rotary motor including the ratchet mechanism, the activablemember, and the operator mechanism.
 13. The apparatus of claim 12,further comprising one or more activable members, the rotary motorfurther including a rotatable sleeve engageable by the activablemembers.
 14. The apparatus of claim 1, further comprising a secondratchet mechanism, the first ratchet mechanism adapted to move theoperator member and the second ratchet mechanism adapted to hold theposition of the operator member.
 15. The apparatus of claim 14, whereinthe first ratchet mechanism is moveable by expansion of the material.16. The apparatus of claim 15, further comprising a spring applying aforce against the first ratchet mechanism in opposition to a forceapplied by the material.
 17. The apparatus of claim 1, wherein theratchet mechanism includes at least a Belleville spring having at leasta sharp edge engageable against a surface of the operator member. 18.The apparatus of claim 1, wherein the ratchet mechanism includes atleast a tablet having at least a sharp edge engageable against a surfaceof the operator member.
 19. The apparatus of claim 18, wherein theoperator member includes a shaft.
 20. A string for use in a wellbore,comprising: a downhole device; and an actuator assembly to operate thedownhole device, the actuator assembly including an expandable materialand an operator member operably coupled to the downhole device, theexpandable material positioned to apply a force against the operatormember when expanded.
 21. The string of claim 20, further comprising acontrol line carrying an input energy to the actuator assembly to causeexpansion of the expandable material.
 22. The string of claim 21,wherein the control line includes one or more electrical conductors. 23.The string of claim 21, wherein the control line includes a waveguide tocarry one of infrared energy and microwave energy.
 24. The string ofclaim 21, wherein the control line includes a fiber optic line to carryone of infrared energy and microwave energy.
 25. The string of claim 20,wherein the downhole device includes a valve.
 26. The string of claim25, wherein the downhole device includes a subsurface safety valve. 27.A method of operating a downhole device in a wellbore, comprising:providing an actuator having an expandable material; and communicatingactivation energy to cause expansion of the expandable material toactivate the actuator.
 28. The method of claim 27, wherein communicatingthe activation energy includes communicating electrical energy.
 29. Themethod of claim 27, wherein communicating the activation energy includescommunicating infrared energy.
 30. The method of claim 27, whereincommunicating the activation energy includes communicating microwaveenergy.
 31. The method of claim 27, wherein communicating the activationenergy includes communicating magnetic energy.
 32. The method of claim27, wherein providing the actuator includes providing an actuator havinga piezoelectric material.
 33. The method of claim 27, wherein providingthe actuator includes providing an actuator having a magnetostrictivematerial.
 34. The method of claim 27, wherein providing the actuatorincludes providing an actuator having a heat-expandable material.
 35. Anapparatus for operating a downhole device in a wellbore, comprising: anactuator having one or more elements expandable or contractable byapplication or removal of input energy; and an operator mechanismoperatively coupled to the actuator.